Determination of trace elements in crude oils by ICP-MS using detergent microemulsion.

A method was developed and evaluated in terms of its analytical performance for the determination of Ti, V, Cr, Mn, Ni, Cu, Mo, Cd, Sn and Pb concentrations in three Libyan crude oil samples using ICP-MS. The samples were introduced to the plasma after the formation of microemulsions in which Triton X-100 was used as the emulsifier and tetralin was the co-solvent with the addition of nitric acid in order to enable calibration with aqueous standard. The validity of the method was proven by three different traditional sample preparation protocols (dry ash, wet digestion and microwave digestion) and good agreement was obtained between the results using the proposed and comparative procedures. The accuracy was confirmed by analysing two different certified reference materials (Used Oil HU-1 from SCP science and Wear Metals in Lubricating Oils 1084a from NIST). The recoveries ranged from 100.1% to 119.9 % for all elements and 85.1 % for Cr in Used Oil HU-1 and from 84.8 % to 100.1 % for all elements and 79.1 % for Cr in 1084a NIST. The precision of the method was < 5% for all elements, except for Cr which was 30.9 %. The limits of detection based on 3 times standard deviation of the blank (10 replicates), were ranging from 0.1 to 0.7 ng g[-1] for all elements and 4.8 ng g[-1] for Cr. The limits of quantification based on 10 times standard deviation of the blank (10 replicates) ranged between 0.2 to 2.4 ng g[-1] and 16.1 ng g[-1] for Cr. Satisfactory recoveries were obtained when 2 mug L[-1] and 10 mug L[-1] multielement spikes were used to test the accuracy of the developed method. The method has proven to be reliable, and can be used in routine analysis in laboratories where there is a high throughput of the sample.